“THROUGHOUT history, poverty is the normal condition of man,” wrote Robert Heinlein, a science-fiction writer. Until the 18th century, global GDP per person was stuck between $725 and $1,100, around the same income level as the World Bank’s current poverty line of $1.90 a day. But global income levels per person have since accelerated, from around $1,100 in 1800 to $3,600 in 1950, and over $10,000 today.
一个名为罗伯特·海因莱因（ Robert Heinlein ）的科幻作家写到，“纵观历史，贫穷是人们的常态”。直到18世纪，全球GDP每人都卡在725美元和1100美元之间，大约和世界银行目前每天1.90美元贫困线一样。但是全球收入水平每人已经增长了，从1800年1100美元到1950年3600美元，到今天超过了10万美元。
Economists have long tried to explain this sudden surge in output. Most theories have focused on the factors driving long-term economic growth such as the quantity and productivity of labour and capital. But a new paper* takes a different tack: faster growth is not due to bigger booms, but to less shrinking in recessions. Stephen Broadberry of Oxford University and John Wallis of the University of Maryland have taken data for 18 countries in Europe and the New World, some from as far back as the 13th century. To their surprise, they found that growth during years of economic expansion has fallen in the recent era—from 3.88% between 1820 and 1870 to 3.06% since 1950—even though average growth across all years in those two periods increased from 1.4% to 2.55%.
经济学家长久以来一直试图解释这种收入上的突然增长。大部分理论都集中在促进经济长期增长的因素如劳动和资本的质量和生产力。牛津大学的斯蒂芬·布劳德伯利（Stephen Broadberry）和马里兰大学的约翰·沃利斯（John Wallis）把18世纪欧洲和新世界，还有一些早至13世纪的数据收取了。令他们吃惊的是，他们发现经济扩张时期的经济增长在最近时期已经下降—从1820年和1870年的3.88%到自1950年3.06%—即使这两个时期中这些年份平均经济增长从1.4%上升到2.55%。
Instead, shorter and shallower
slumps
led to rising long-term growth. Output fell in a third of years between 1820 and 1870 but in only 12% of those since 1950. The rate of decline per recession year has fallen too, from 3% to 1.2%.
相反，时间更短，程度更浅的经济衰退导致了长期的经济增长。收入在1820年和1870年中三分之一的年份下降，但是自从1950年仅在12%的年份中下降。每个经济衰退年份下降的比率也从3%降低到了1.2%。
